Process for the preparation of a C20 to C60 wax from the selective thermal decomposition of plastic polyolefin polymer

ABSTRACT

The present invention relates to a process for the preparation of a C 20  to C 60  wax from the thermal decomposition of plastic polymer. The present invention provides a vacuum pyrolysis process for preparing a C 20  to C 60  wax from the thermal decomposition of plastic polyolefin polymer, the method comprising the steps of: i) introducing plastic polyolefin polymer into a thermal reaction zone of a vacuum pyrolysis reactor; ii) heating the plastic polyolefin polymer at sub-atmospheric pressure, wherein the temperature in the thermal reaction zone of the reactor is from 500° C. to 750° C., to induce thermal decomposition of the plastic polyolefin polymer and to form a thermal decomposition product effluent which comprises a major portion by weight of a C 20  to C 60  wax fraction; and iii) condensing a vapour component of the thermal decomposition product effluent from the vacuum pyrolysis reactor in a multistage condensation comprising a plurality of condensation stages connected in series.

The present invention relates to a process for the preparation of a C₂₀to C₆₀ wax from the thermal decomposition of plastic polymer. Inparticular, the present invention corresponds to a vacuum pyrolysisprocess which is operated under conditions favourable for the formationof a C₂₀ to C₆₀ wax.

As levels of waste plastic continue to rise globally, there has becomean increasing focus on plastics recycling solutions as an alternative tolandfill. Plastic recycling has historically been focused on producingfuel oil and gas products, although conversion of waste plastics intowaxes, lubricants and grease base stocks is also possible. There remainsa strong market for waxes as a result of a diverse range of possibleapplications including, for example, use in adhesives, candles, buildingmaterials, electrical insulation materials, paper and cardboard surfacetreatments as well as in paints and other coatings. Waxes may also bereadily converted into lubricant oils which are of particular value tothe automotive industry. Thus, given the healthy demand for waxes, itwould be advantageous to recycle the large volumes of waste plastic thatcontinue to be generated in order to prepare waxes which are ofsignificant commercial value.

Pyrolysis is a well-known thermochemical decomposition process whichoccurs in the absence of oxygen. Historically, pyrolysis has been usedas a means for conversion of organic material into higher valuedecomposition products. Common examples include conversion oflignocellulosic biomass into bio-oil and the recycling of used rubbertyres into fuel oil and gas products. Pyrolysis has also been used as ameans for converting waste plastic into wax and other higher valuedecomposition products.

A number of different processes and reactor designs have beeninvestigated for the pyrolysis of waste plastics, including processesutilising melting vessels, blast furnaces, autoclaves, tube reactors,rotary kilns, cooking chambers and fluidized bed reactors. Much of thefocus regarding waste plastics pyrolysis has been directed to fluidisedbed processes. Fluidized bed reactors have been popular as they providerapid heat transfer, good control for pyrolysis reaction and vapourresidence time, extensive high surface area contact between fluid andsolid per unit bed volume, good thermal transport inside the system andhigh relative velocity between the fluid and solid phase, as well as anease of use. For these reasons, fluidized-bed reactors can also beoperated so as to provide so called “fast pyrolysis” conditions,characterised by very high heating and heat transfer rates and lowvapour residence times in the thermal decomposition zone of thepyrolysis reactor which is intended to minimise secondary crackingreactions in the reactor.

EP 0502618 discloses a process for pyrolysing polyolefins in a fluidisedbed of particulate material (e.g. quartz sand) and with a fluidising gasat a temperature of from 300 to 690° C., preferably without a catalystand at atmospheric pressure. The pyrolysis products comprise lowerhydrocarbons, preferably in the range of around C₇ to C₇₀. EP 0 567 292relates to a similar fluidised bed process but is conducted at higherpressures and in the presence of an acidic catalyst such as an aluminaor zeolite catalyst.

EP 0577279 discloses the use of a toroidal fluidised bed reactor inplace of a conventional fluidised bed. A larger size range ofparticulate bed materials can be used with this process and lowresidence times can be implemented. At 350° C., in a bed of alumina, amixture of hydrocarbons was formed by pyrolysis of polyethylene, mainlyhaving 30 to 40 carbon atoms. At 500° C., and using a zirconia bed, theresult was mainly 40 to 80 carbon atoms.

EP 0687692 discloses another fluidised bed process with the addition of“guard beds” comprising CaO to remove HCl from the product beforefurther processing. This process can be used with “mixed waste plastic”which includes, for instance, PVC. Pre-conditioning can include heatingat 250 to 450° C. in a stirred tank or extruder. It is also disclosed tointroduce liquid (molten) hydrocarbons (from the fluidised bed, orrefinery streams) to the feedstock in order to further crack thesehydrocarbons and to reduce viscosity/improve heat transfer.

EP 0620264 discloses a fluidized-bed pyrolysis process, wherein a waxproduct is subsequently hydrotreated to remove double-bonds andheteroatoms after pyrolysis, before being isomerised and fractionated togive a lubricating oil.

Other processes for conversion of waste plastics have focused oncatalytic depolymerisation, an example of which is disclosed in WO2014/110664. In that process, a pre-heated molten polymeric material,such as polyethylene, is heated in a high pressure reactor in thepresence of [Fe—Cu—Mo—P]/Al₂C₃ catalyst in order to produce the desiredwax product.

DE 100 13 466 discloses a process for recovery of high molecular weightpolyolefin decomposition wax from recycled plastics. In that process,waste plastics are melted at temperatures ranging from 350° C. to 390°C. before the melted plastic is thermally decomposed at temperatures upto 450° C. in the absence of oxygen. Distillation, preferably undervacuum, is then undertaken to isolate the desired high molecular weightfraction. This document teaches the use of melting followed by pyrolysisat temperatures of up to a maximum of 450° C. and under the pressuregenerated by the reaction. There is no suggestion of reducing thepressure at which pyrolysis is conducted in this document. However, sucha reduction would also be expected to reduce the heating requirement ofthe pyrolysis reaction in order to achieve the same level of cracking,since the boiling point of the polyolefin material is reduced at lowerpressure.

An alternative pyrolysis process that has been used in connection withthe thermal decomposition of biomass is vacuum pyrolysis. This processobviates the use of a carrier gas which is required in other pyrolysisprocesses. Carrier gas can entrain fine char particles produced fromdecomposition of biomass in the reactor, which are subsequentlycollected with the oil when it condenses; impacting negatively uponbio-oil quality. Vacuum pyrolysis can therefore help improve bio-oilquality by reducing entrainment of fine char particles. The vacuumpyrolysis process can also accommodate larger feed particles thanconventional fluidized bed processes.

The heat transfer rates in vacuum pyrolysis are typically lower comparedwith fluidised bed processes and other pyrolysis technologies and onthis basis vacuum pyrolysis is generally considered to correspond to aso called “slow pyrolysis” process, characterised by relatively slowheating rates (approximately 0.1-1° C./s) as opposed to a so called“fast pyrolysis” process characterised by fast heating rates(approximately 10-200° C./s). Nevertheless, the produced pyrolysisvapours are quickly removed from the vacuum pyrolysis reactor as aresult of the vacuum, thereby reducing secondary cracking reactions.Consequently, vacuum pyrolysis may also be considered to simulate a“fast pyrolysis” process at least to this extent. Such a process is, forexample, disclosed in CA 1,163,595 which describes vacuum pyrolysis oflignocellulosic materials to afford organic products and liquid fuels.An overview of fast pyrolysis of biomass is also provided in BridgewaterA. V. et al., Organic Geochemistry, 30, 1999, pages 1479 to 1493.

There remains a need for alternative pyrolysis processes which areadvantageous for the thermal decomposition of plastic polymer,especially where a wax pyrolysis product can be prepared in high yield.

It has now been found that the simulated fast pyrolysis conditions ofvacuum pyrolysis may be applied advantageously to the selective thermaldecomposition of waste plastic for production of C₂₀ to C₆₀ wax. Inparticular, the present invention utilises a vacuum pyrolysis processwith a multistage downstream condensation, the combination of which hasbeen found to minimise secondary cracking reactions both in and outsidethe reactor thereby helping to maximise yield of a C₂₀ to C₆₀ waxproduct. Numerous additional advantages of the process of the presentinvention will be apparent from the below disclosure.

By employing a vacuum pyrolysis process in the thermal decomposition ofplastic polymer in accordance with the present invention, rather than aconventional high-pressure fluidized-bed pyrolysis process, it ispossible to obtain C₂₀ to C₆₀ wax of particularly desirable compositionand in good yield. The process of the invention may be used to obtain asynthetic wax having desirable properties such as favourable melting,congealing, and drop points, as well as favourable viscosity, density,and needle penetration.

A benefit of the present invention is that it simulates a fast pyrolysisprocess so as to minimise secondary cracking reactions in the pyrolysisreactor, which has been found to be beneficial for maximising C₂₀ to C₆₀wax yield, yet does not have the energy demand associated with therelatively high heating rates utilised, for instance, in fluidized-bedfast pyrolysis processes. In other words, the present invention canrepresent an economical solution to obtaining a selective thermaldecomposition of plastic polymer so as to produce a high value waxpyrolysis product in good yield. The process of the present inventiondoes not require the use of a catalyst, a carrier gas or a fluidized-bedwhich typically requires intermittent regeneration, maintenance andrepair to maintain adequate functionality.

Furthermore, the multistage condensation utilised for condensing thepyrolysis effluent has been found to be advantageous for minimisingsecondary cracking reactions whilst the step-wise cooling associatedwith the multistage condensation corresponds to an economical use ofcooling, as well as a means for separation of some lighter boiling pointfractions from the condensate comprising the C₂₀ to C₆₀ wax product.

Thus, in one aspect the present invention provides a vacuum pyrolysisprocess for preparing a C₂₀ to C₆₀ wax from the thermal decomposition ofplastic polyolefin polymer, the method comprising the steps of:

-   -   i) introducing plastic polyolefin polymer into a thermal        reaction zone of a vacuum pyrolysis reactor;    -   ii) heating the plastic polyolefin polymer at sub-atmospheric        pressure, wherein the temperature in the thermal reaction zone        of the reactor is from 500° C. to 750° C., to induce thermal        decomposition of the plastic polyolefin polymer and to form a        thermal decomposition product effluent which comprises a major        portion by weight of a C₂₀ to C₆₀ wax fraction; and    -   iii) condensing a vapour component of the thermal decomposition        product effluent from the vacuum pyrolysis reactor in a        multistage condensation comprising a plurality of condensation        stages connected in series.

A plastic polyolefin polymer is employed for thermal decomposition inaccordance with the present invention and is intended to include anysuitable thermoplastic polymer preparable from the polymerisation of asimple olefin monomer. Examples include polyethylene (PE), polypropylene(PP), polymethylpentene (PMP), polybutene-1 (PB-1), as well ascopolymers thereof.

Preferably, the plastic polyolefin polymer employed as the feed inaccordance with the present invention comprises or consists essentiallyof used or waste plastic. Nevertheless, in some embodiments the plasticpolyolefin polymer employed as the feed may include virgin plastic, ormay even consist essentially of virgin plastic.

In addition to polyolefins, common sources of waste plastic materialinclude: aromatic plastic polymers, for example polystyrene; halogenatedplastic polymers, for example polyvinyl chloride andpolytetraflouroethylene; and polyester plastic polymers, for examplepolyethylene terephthalate. It is preferred that these plastic polymersare kept to a minimum in the feed which is subjected to pyrolysis in theprocess of the present invention. The presence of appreciable quantitiesof these polymers can complicate system design and feasibility. Forexample, these polymers can lead to gum formation necessitating regularreactor shut-down and cleaning steps to be implemented. Halogenatedpolymers also give rise to the formation of haloacids followingpyrolysis which can lead to significant corrosion problems unless stepsare taken to neutralise or otherwise trap the acid byproducts.

Thus, in preferred embodiments, the feed to the pyrolysis reactorcomprises less than 1.0 wt. %, preferably less than 0.1 wt. %, ofcombined aromatic, halogenated and polyester polymers. Most preferably,the feed to the pyrolysis reactor comprises substantially no aromatic,halogenated and polyester polymers. Where used or waste plastic is usedas the source of the plastic polyolefin polymer utilized in the presentinvention, it will be appreciated that sorting processes are availableto substantially eliminate contamination of the waste polyolefinplastic.

The plastic polyolefin polymer used in accordance with the presentinvention preferably comprises polyethylene, which may be in the form ofhigh-density polyethylene (HDPE), low-density polyethylene (LDPE),linear low density polyethylene (LLDPE) or mixtures thereof.

The plastic polyolefin polymer used in accordance with the presentinvention may comprise polypropylene, which may be in the form ofhigh-density polypropylene (HDPP), low-density polypropylene (LDPP) ormixtures thereof.

In preferred embodiments, the plastic polyolefin polymer comprises bothpolyethylene and polypropylene. For example, the plastic polyolefinpolymer may comprise polyethylene and polypropylene in a weight ratio ofpolyethylene to polypropylene of from 30:70 to 90:10. In preferredembodiments, the plastic polyolefin polymer comprises polyethylene andpolypropylene in an amount of at least 90 wt. %, more preferably atleast 95 wt. %, most preferably at least 97 wt. %.

In particularly preferred embodiments, the weight ratio of polyethyleneto polypropylene is from 60:40 to 90:10, more preferably from 65:35 to85:15, even more preferably from 70:30 to 80:20. It is has been foundthat a particularly desirable wax may be produced by the vacuumpyrolysis process of the present invention when the plastic polymer feedcomprises polyethylene and polypropylene in these preferred weightratios. In particular, these preferred ratios have been found to afforda wax with particularly favourable properties including melting,congealing, and drop points, as well as favourable viscosity, density,and needle penetration, as compared to other polymer mixtures, includingmixtures of polyethylene and polypropylene which do not have theseweight ratios.

The beneficial effect of these preferred ratios is believed to berelated to the particular olefin versus paraffin content of the waxproduced by the process of the present invention, which in turn is alsoaffected by the extent of secondary cracking reactions occurring in thepyrolysis reactor, which are kept to a minimum. The presence ofpolypropylene ensures that decomposition products obtained therefrominclude branching, which can have a significant effect on the physicalproperties of the wax obtained.

Another benefit associated with the presence of branching relates todownstream processing where the wax product of the process of thepresent invention is converted into, for instance, a lubricant basestock. In order to improve lubricant properties, including for examplereducing pour point and increasing viscosity index, isomerization istypically included to introduce branching. The presence of branching inthe wax product of the thermal decomposition (derived, for instance,from the presence of polypropylene in the plastic polyolefin polymerfeed) can make the downstream isomerization step less onerous or energyintensive. For example, an isomerization catalyst which has highselectivity for n-paraffins, meaning that there is preference forisomerization of the portion of the wax which requires it, may beadvantageously used under energetically favourable conditions whichwould not be sufficient for the effective conversion of other waxes notcontaining branching (for example polyethylene or Fischer-Tropschderived waxes) to lubricant base stocks.

In order to obtain a plastic polyolefin polymer of the desiredcomposition, in preferred embodiments, an optical sorting process isused to select the plastic polyolefin polymer constituents and theirrelative proportions in the polymer feed. Following intermediate sortingprocesses which, for instance, separate different plastics based ondensity or differential buoyancy in air to produce intermediate streams,optical sorting may subsequently be used to further sort the componentsof a single intermediate stream. Optical sorting is a convenient meansfor ensuring that the desired ratio of polyethylene to polypropylene inthe plastic polyolefin polymer fed to the pyrolysis reactor ismaintained in the preferred embodiments of the invention. Opticalsorting technologies include near-Infrared (NIR) absorptionspectroscopy, camera color sorters and X-ray fluorescence, as forinstance described in US 2014/0209514 and U.S. Pat. No. 5,134,291.

In step i) of the process of the invention, the plastic polyolefinpolymer is supplied to the thermal reaction zone of the vacuum pyrolysisreactor. The plastic polyolefin polymer may be supplied to the pyrolysisreactor in any form tolerated by the pyrolysis reactor. For example,where the plastic polyolefin polymer is supplied in solid form, this maysuitably be in flaked, pelletized or granular form. However, it ispreferred that the plastic polyolefin polymer is supplied to thepyrolysis reactor in molten form following a pre-heating step.

The plastic polyolefin polymer may be introduced into the pyrolysisreactor by any suitable means, although preferably a means which iscompatible with supplying a vacuum pyrolysis reactor during operationunder sub-atmospheric conditions, potentially on a continuous basis. Inpreferred embodiments, an extruder is used for feeding the plasticpolyolefin polymer to the pyrolysis reactor. Examples of suitableextruders include single or twin screw type, although single screw ispreferred. Where the plastic polyolefin polymer is supplied to thepyrolysis reactor in molten form, the extruder may be heated such thatthe plastic is melted during extrusion.

Thus, in the process of the present invention plastic polyolefin polymermay be supplied to the extruder from a hopper, for instance in flaked,pelletized or granular form, after which it comes into contact with therotating screw which forces the plastic polyolefin polymer along thebarrel of the extruder, which in preferred embodiments is heated. Theplastic polyolefin polymer is subsequently forced through a feed pipeconnected to the inlet of the pyrolysis reactor which allows theextruded plastic to be introduced to the thermal reaction zone of thereactor. In preferred embodiments, the extruder is connected to thepyrolysis reactor via a shut-off valve which intermittently allows feedto enter.

The reactor used in the process of the present invention is a vacuumpyrolysis reactor, which may be of any suitable form provided it may beoperated under sub-atmospheric conditions. As will be appreciated by theskilled person, operating at a vacuum requires certain feed anddischarge configurations in order to maintain a good seal at all times,which configurations, and the associated design implications, are wellknown to the skilled person.

Examples include simple furnace, tank, stirred tank or tube reactors(depending on the scale of the process), as well as moving bed vacuumpyrolysis reactors or stirred bed vacuum pyrolysis reactors. As will beappreciated by the skilled person, stirred tank moving and stirred bedconfigurations complicate reactor design and increase capital costsassociated with the pyrolysis process. Consequently, simple tankreactors may be preferred from a cost perspective.

Vacuum conditions can be used to decrease the boiling point ofcomponents subjected to heating and therefore the vacuum pyrolysis canreduce the heating duty that would otherwise be required for thermaldecomposition of the plastic polyolefin polymer. It has beensurprisingly found that the nature of the thermal decomposition in thevacuum pyrolysis process of the present invention favours the formationof C₂₀ to C₆₀ wax. This is believed to be a consequence of therelatively slow heat transfer conditions and short vapour residencetimes in the reactor associated with the vacuum pyrolysis of the presentinvention, as well as the nature of the condensation stage which hasbeen found to enhance C₂₀ to C₆₀ wax yield and the advantageousproperties of the wax obtained. These properties include the particularolefin versus paraffin content of the wax produced in step ii) of theprocess of the present invention, as well as other compositional traitsresulting from the extent of cracking reactions occurring in thepyrolysis reactor.

Any suitable temperature and pressure combination may be utilized in theprocess of the invention in order to produce a C₂₀ to C₆₀ wax, providedthat it is sufficient for thermal decomposition of the polyolefinplastic polymer to produce pyrolysis vapours. The skilled person is ableto select suitable temperatures and sub-atmospheric pressures asnecessary. For instance, the skilled person will appreciate that atlower pressures, there is a lower heating duty for thermaldecomposition, such that lower temperatures in the thermal reaction zoneof the pyrolysis reactor are required. Conversely, where higherpressures are used, correspondingly higher temperatures may be requiredfor adequate thermal decomposition over a reasonable timeframe.

Any suitable means of which the person of skill in the art is aware forheating the vacuum pyrolysis reactor may be used in connection with theprocess of the present invention, for example a burner and/or aninduction heater.

Suitably, the temperature within the thermal reaction zone of the vacuumpyrolysis reactor is from 500° C. to 750° C. Preferably the temperaturewithin the thermal reaction zone of the vacuum pyrolysis reactor is from500° C. to 650° C., more preferably 525° C. to 650° C., even morepreferably from 550° C. to 650° C., for example from 575° C. to 625° C.

In other examples, the temperature in the thermal reaction zone of thevacuum pyrolysis reactor is greater than 500° C., for example greaterthan 525° C. or greater than 550° C. In other examples, the temperaturein the thermal reaction zone of the vacuum pyrolysis reactor is lessthan 750° C., for example less than 725° C. or less than 700° C.Suitable pressures within the thermal reaction zone of the vacuumpyrolysis reactor are less than 75 kPa absolute. Preferably, thepressure within the thermal reaction zone of the vacuum pyrolysisreactor is less than 50 kPa absolute, more preferably less than 30 kPaabsolute.

It has been found that, by reducing the pressure in the thermaldecomposition zone of the pyrolysis reactor, pyrolysis vapour residencetime decreases. As a result, fewer secondary cracking reactions areobserved and the distribution of constituents of the thermaldecomposition product shifts to higher carbon numbers. Similarly, it hasalso been that, by increasing the temperature in the thermaldecomposition zone of the pyrolysis reactor, the distribution ofconstituents of the thermal decomposition product shifts to highercarbon numbers. This is a consequence of an increase in the volatilityof higher boiling (higher carbon number) components inside the pyrolysisreactor as the pyrolysis temperature increases coupled with the lowvapour residence time in the pyrolysis reactor, which minimisessecondary cracking reactions associated with these higher boiling pointcomponents.

The thermal decomposition product effluent produced in accordance withthe present invention comprises a vapour component and in someembodiments may consist solely of a vapour component. Nevertheless, asthe process of the present invention reduces secondary crackingreactions during the pyrolysis, the products of primary crackingreactions, for instance, may be liquids under the conditions of thepyrolysis. However, such liquid products may be entrained as part of anaerosol (e.g. a mist or a fog) within the pyrolysis vapours, orotherwise mobilized by the pyrolysis vapours, and therefore may be sweptout of the pyrolysis reactor along with the pyrolysis vapours by thevacuum. Thus, where reference is made herein to the residence time ofpyrolysis vapours in the thermal reaction zone of the reactor, this isalso intended to refer to the residence time of an aerosol of liquidthermal decomposition product entrained within pyrolysis vapours, or anyother association of liquid thermal decomposition product and pyrolysisvapours where pyrolysis vapours assist in mobilizing liquid thermaldecomposition product out of the reactor.

As discussed in hereinbelow, the effect of reducing secondary crackingreactions is also enhanced when a multistage condensation immediatelyfollows the pyrolysis step. The multistage condensation has been foundto provide an efficient cooling gradient over the plurality of connectedcondensation stages, which set-up has been found to be particularlysuited to a fast flow of vapours, as in the case of vacuum pyrolysis.The multistage condensation provides effective cooling and condensing ofpyrolysis vapours whilst reducing the overall refrigeration power demandassociated with the use of only a single condensation unit.

In preferred embodiments, the temperature within the thermal reactionzone of the vacuum pyrolysis reactor is from 600° C. to 750° C. and thepressure within the thermal reaction zone of the vacuum pyrolysisreactor is less than 50 kPa absolute.

In preferred embodiments, the temperature within the thermal reactionzone of the vacuum pyrolysis reactor is from 500° C. to 750° C. and thepressure within the thermal reaction zone of the vacuum pyrolysisreactor is less than 30 kPa absolute.

In preferred embodiments, the temperature within the thermal reactionzone of the vacuum pyrolysis reactor is from 500° C. to 750° C. and thepressure within the thermal reaction zone of the vacuum pyrolysisreactor is less than 10 kPa absolute.

Under these preferred pyrolysis conditions, it is has been found thatthe process of the present invention is particularly advantageous interms of the yield and quality of the C₂₀ to C₆₀ wax fraction that maybe produced. In this case, the residence time of the pyrolysis vapoursin the thermal decomposition zone of the reactor is particularly short(for example, 1 to 5 seconds). As the skilled person will appreciate,vapour residence time in a vacuum pyrolysis reactor may be determinedfrom knowledge of the rate constant for the pyrolysis reaction and basedon gas flow meter measurements at the reactor outlet. The benefits ofoperating under these conditions are enhanced by the multistagecondensation step of the process, which preferably includes only two orthree condensation stages connected in series having successively lowertemperature, discussed in more detail below.

In step iii) of the process, pyrolysis vapours produced in the pyrolysisreactor are condensed to afford the condensed product of the pyrolysisreaction. It has been found to be beneficial to C₂₀ to C₆₀ waxcondensate isolation and yield if a multistage condensation of thepyrolysis vapours is undertaken. This can help to minimise secondarycracking reactions. This is believed to be because there is moreefficient cooling and condensing of the pyrolysis vapours over thecooling gradient established by the series of condensation stages than,for instance, in the case where only a single condensation unit isutilised. The pyrolysis vapours flow relatively quickly through thesystem, as would be expected in the case of a fast pyrolysis process, asa result of the vacuum. The presence of a plurality of condensationstages has been found to be particularly suited for cooling the fastflowing vapours and enhancing the beneficial effects of the pyrolysis interms of composition and yield of the wax product. Furthermore, themultistage condensation has been found to be more economical in terms ofcooling power expended during the condensation than single unitcondensation processes.

It has also been found that at higher pyrolysis temperatures, forexample temperatures of 500° C. and above, that, while an increasedproportion of C₂₀-C₆₀ waxes is produced, at the same time a largerproportion of lighter (below around C₁₀) hydrocarbons is also produced.By providing a multistage condensation in combination with a higherpyrolysis temperature, e.g. 500° C. to 750° C., improved separation ofthis increased lighter fraction from the desired heavy wax fraction canbe achieved in comparison to a single stage condensation. Therefore, theuse of the combination of higher pyrolysis temperatures and multistagecondensation for the production and separation of the desirable waxfractions provides synergistic effects in terms of yield of the desiredC₂₀-C₆₀ wax fraction. It will be understood that convenient separationof lighter fractions during condensation may simplify or eliminate anydownstream distillation requirements.

Reference to a multistage condensation is intended to refer tocondensation in which at least two separate condensation stagesconnected in series are utilised, and where each condensation stage inthe series is operated at successively lower temperature (i.e. coolanttemperature is lowest at the final condensation stage).

The multistage condensation includes at least two condensation stagesconnected in series which operate at successively lower temperatures.Preferably, the first condensation stage, which is closest to thepyrolysis reactor, includes a collection vessel for holding condensateformed in the first condensation stage. Alternatively, the firstcondensation stage may be configured such that liquid condensate as wellas residual pyrolysis vapours are passed onto the second condensationstage in the series, which is equipped with a collection vessel tocollect condensate from both first and second condensation stages.

At least partial condensation occurs in the first condensation stagebefore the remaining pyrolysis vapours are passed to the secondcondensation stage. Preferably, substantially all of the C₂₀ to C₆₀ waxfraction is collected in a collection vessel of the first condensationstage. The collection vessel of the first condensation stage may includean outlet through which condensate may be conveniently extracted.Typically, the temperature within the first condensation stage issignificantly lower than the pyrolysis reactor, but higher than themelting point of the condensate composition so that a flow of liquidcondensate to the collection vessel remains possible. The secondcondensation stage, which is operated at a lower temperature than thefirst condensation stage, includes a collection vessel for collection ofcondensate, including condensate formed in the first condensation stagein some embodiments. The collection vessel of the second condensationstage may include an outlet through which condensate may be convenientlyextracted. In some embodiments, the second condensation stage is thefinal condensation stage of the series. The final condensation stage isintended to condense substantially all remaining pyrolysis vapours whichcomprise primarily low boiling components. Thus, the final condensationstage may act as a cold trap which reduces or substantially eliminatespyrolysis vapours contacting the vacuum pump located downstream.

As will be appreciated by the skilled person, additional condensationstages may be included such that more than two condensation stagesconnected in series are integrated. For example, additional condensationstages may be included between the first and final condensation stageswith the intention of separating mid-boiling point fractions of thecondensate. In this way, a fractional condensation process may beutilised. Thus, in some embodiments, the multistage condensationconsists of three, four, or even five condensation stages connected inseries. Nevertheless, in preferred embodiments, the multistagecondensation used in the process of the present invention consists oftwo or three condensation stages only, most preferably only twocondensation stages.

In embodiments where more than two condensation stages are connected inseries, the second condensation stage is connected to a thirdcondensation stage which is operated at an even lower temperature thanthe second condensation stage. The third condensation stage may alsoinclude an outlet through which condensate may be convenientlyextracted.

Any suitable condensation apparatus known to the skilled person whichmay be used under sub-atmospheric conditions may be utilised for theindividual condensation stages in the multistage condensation of thepresent invention. Examples of suitable condensation stages includeliquid-cooled surface condensers, which may be operated in transverse,parallel or counter flow. Other condensation stages may be configured asquench units, for example a demister quench unit or quench tower. Inpreferred embodiments, the first condensation stage corresponds to ademister quench unit or quench tower.

In some embodiments, such quench units or towers may be operated with adirect liquid quench in which a liquid coolant contacts the thermaldecomposition product directly. Suitable coolant liquids for thispurpose include liquid propane and supercritical carbon dioxide. When adirect liquid quench is used, the coolant liquid may be convenientlyseparated from the thermal decomposition product by lowering pressure toboil off the coolant, which may then be captured for recycle. Directliquid quench is advantageous for rapidly condensing the thermaldecomposition product so as to minimise secondary cracking reactions.Consequently, where a direct liquid quench is employed, this ispreferably as part of the first condensation stage.

In some embodiments, the temperature of the coolant liquid associatedwith the first stage may be from 65° C. to 120° C., for example from 75°C. to 100° C., or from 85° C. to 95° C. As will be appreciated by theskilled person, a temperature gradient will exist over the flow paththrough the condensation stage which differs from the temperature of thecoolant. Nevertheless, the degree of cooling within the first stage isto the extent that at least partial condensation of pyrolysis vapoursoccurs.

In some embodiments, the temperature of the coolant liquid(s) associatedwith the second and any optional additional intermediate condensationstages, may be from 0° C. to 65° C., for example from 25° C. to 50° C.,or from 35° C. to 45° C.

In some embodiments, the temperature of the coolant liquid associatedwith the last condensation stage may be from −200° C. to 25° C., forexample −80° C. to 15° C. or −25° C. to 10° C.

In other embodiments, lower temperatures are used in connection with thefirst and second condensation stages. For example, in some embodiments,the temperature of the coolant liquid associated with the firstcondensation stage may be from −20° C. to 50° C., for example from −15°C. to 30° C., or from −10° C. to 10° C. In some embodiments, thetemperature of the coolant liquid(s) associated with the second and anyoptional additional intermediate condensation stages, may be from −30°C. to 10° C., for example from −25° C. to 0° C., or from −20° C. to −10°C. As will be appreciated, lower temperatures in the condensation stagesare however associated with higher energy costs.

As will be appreciated by the skilled person, the coolant liquid used ateach condensation stage will depend on the temperature at which thecoolant is intended to be operated, which may be optimised for theparticular conditions of the process, for example reactor temperatureand system pressure. Examples of suitable coolants include water oraqueous coolants, hydrocarbon-based coolants, for example propane orglycol, or inorganic coolants such as liquid nitrogen. The skilledperson is able to select an appropriate coolant depending on the desiredtemperature of operation, or indeed if a direct liquid quench isutilised. For example, glycol or liquid nitrogen may be utilized for thecold trap of the final condensation stage, if desired and suitable forthe scale of the process.

Any suitable vacuum pump may be used in connection with the process ofthe present invention. An example of such a pump includes an oil pump.In order to avoid damage to the pump used in the process of theinvention, where haloacids are produced during the pyrolysis as a resultof the presence of a minor amount of halogenated polymers in the feed, acalcium oxide guard bed may be used upstream of the vacuum pump.

Following the multistage condensation step of the process of the presentinvention, a condensate is typically obtained comprising a major portionof C₂₀ to C₆₀ wax, typically together with an amount of a lighter dieselfraction. Thus, the process of the present invention may furthercomprise a step iv) of fractionating the thermal decomposition producteffluent (i.e. the liquid/condensed portion of the thermal decompositionproduct effluent) in order to obtain a C₂₀ to C₆₀ wax fractionsubstantially free of lighter and/or heavier thermal decompositionproducts. As the skilled person will be aware, the fractionation may,for instance, be undertaken in a flash vessel operating under reducedpressure or a distillation column. The distillation column may be aconventional distillation column with a number of stages (e.g. idealstages) commensurate with the separation desired, for example betweenabout 5 and about 50 ideal separation stages.

Lighter fractions, for instance including the diesel fraction, obtainedfrom the fractionation step may be used as a fuel source for thepyrolysis reactor. Where fractionation of the condensed product of theinvention containing C₂₀ to C₆₀ wax affords a fraction containing amajor portion of heavier (i.e. larger carbon number) components, thisfraction may be recycled to the vacuum pyrolysis reactor for furtherthermal decomposition.

It will be appreciated that by including a multistage condensation aspreviously described, the convenient separation of lighter fractionsduring condensation may simplify or eliminate these distillationrequirements. Nonetheless, it will be understood that lighter fractionsseparated during the condensation may also be used as a fuel source forthe pyrolysis reactor or heavier fractions from the condensation couldbe recycled to the pyrolysis reactor.

By means of the process of the present invention, it is possible toobtain the C₂₀ to C₆₀ wax fraction as the major portion of the totaleffluent from the pyrolysis reactor. As the skilled person willappreciate, a major portion is intended to refer to over 50 wt. % of theeffluent from the pyrolysis reactor. In preferred embodiments, the C₂₀to C₆₀ wax product represents over 55 wt. %, more preferably over 60 wt.%, even more preferably over 65 wt. %, still more preferably over 70 wt.% of the total effluent from the pyrolysis reactor.

The C₂₀ to C₆₀ wax fraction produced by the process of the presentinvention typically comprises a mixture of olefins and n-/iso-parrafins.In some embodiments, the C₂₀ to C₆₀ wax fraction comprises from 20 wt. %to 80 wt. % olefins, preferably from 40 wt. % to 70 wt. % olefins, morepreferably from 45 to 65 wt. % olefins. These ranges may apply to thecontent of 1-olefins, or the combined amount of all olefins present,preferably to the content of 1-olefins only. The C₂₀ to C₆₀ wax fractionof the present invention may include a higher olefin content than wouldbe expected from the pyrolysis of plastic polyolefin polymer due to thereduction in the level of secondary cracking reactions occurring duringthe process of the present invention. Thus, there is an increasedlikelihood of thermal decomposition leading to cracking which does noteliminate the presence of double bonds in the carbon chains of theproduct compared to alternative processes.

In some embodiments, the C₂₀ to C₆₀ wax fraction of the process of theinvention comprises at least 50 wt. %, preferably at least 75 wt. %,more preferably at least 85 wt. %, even more preferably at least 90 wt.% of a C₂₅ to C₅₅ wax sub-fraction.

In some embodiments, the C₂₀ to C₆₀ wax fraction of the process of theinvention comprises at least 50 wt. %, preferably at least 75 wt. %,more preferably at least 85 wt. %, even more preferably at least 90 wt.% of a C₂₅ to C₅₀ wax sub-fraction.

In some embodiments, the C₂₀ to C₆₀ wax fraction of the process of theinvention comprises at least 50 wt. %, preferably at least 75 wt. %,more preferably at least 85 wt. %, even more preferably at least 90 wt.% of a C₃₀ to C₄₅ wax sub-fraction.

In other embodiments, the C₂₀ to C₆₀ wax fraction of the process of theinvention comprises at least 50 wt. %, preferably at least 75 wt. %,more preferably at least 90 wt. %, even more preferably at least 90 wt.% of a C₃₀ to C₄₀ wax sub-fraction.

In other embodiments, the C₂₀ to C₆₀ wax fraction of the process of theinvention comprises at least 50 wt. %, preferably at least 75 wt. %,more preferably at least 85 wt. %, even more preferably at least 90 wt.% of a C₃₀ to C₃₅ wax sub-fraction.

As described herein before, the C₂₀ to C₆₀ wax fraction of the processof the invention has been found to have particularly beneficialproperties, including melting, congealing, and drop points, as well asfavourable viscosity, density, and needle penetration. In particular,the C₂₀ to C₆₀ wax fraction of the invention has generally been found tohave superior properties to synthetic waxes, for example Fischer-Tropschwaxes.

It has also been surprisingly found that the benefits of the process ofthe invention in terms of the properties of the C₂₀ to C₆₀ wax fractionobtained are even further enhanced when a particular composition ofplastic polyolefin polymer is used for thermal decomposition. Inparticular, in preferred embodiments where a combination of polyethyleneand polypropylene is used as the plastic polyolefin polymer,specifically where the weight ratio of polyethylene to polypropylene isfrom 60:40 to 90:10, preferably from 65:35 to 85:15, more preferablyfrom 70:30 to 80:20, it is has been found that a superior wax product isobtainable.

In particular, it has been surprisingly found that increasing pyrolysistemperature has a greater effect on the proportion of C₂₀-C₆₀ waxproduced for polypropylene and polyethylene/polypropylene mixed feedsthan for a pure polyethylene polymer feed. In particular, increasingpyrolysis temperature, for instance at 500° C. and above, can lead to agreater increase in the yield of C₂₀-C₆₀ wax for a pure polypropylene ormixed polyethylene/polypropylene feed than when compared to the effectof the same pyrolysis temperature increase in the case of purepolyethylene feed. Thus, by using a mixed feed comprising polypropyleneand polyethylene, the benefits of operating the pyrolysis at hightemperature, for example temperatures above 500° C., in terms of theC₂₀-C₆₀ fraction yield may be obtained whilst also at the same timeretaining the benefits of including some branching in the waxes, asdiscussed hereinbefore. Thus, for producing waxes with desirableproperties, the synergy between the use of a certain proportion ofpolypropylene in the feed, particularly in the ranges describedhereinbefore, and the use of higher pyrolysis temperatures can beparticularly advantageous.

In preferred embodiments, the melt point of the C₂₀ to C₆₀ wax fractionwhich is obtained from the process of the present invention is from 45to 80° C., more preferably from 60 to 75° C. The melt point may suitablybe determined by ASTM Method D87. Alternatively, where the C₂₀ to C₆₀wax fraction does not show a characteristic melting plateau, the dropmelt point of the C₂₀ to C₆₀ wax fraction which is obtained from theprocess of the present invention is from 45 to 80° C., more preferablyfrom 50 to 70° C. Drop melt point may suitably be determined by ASTMMethod D127.

In preferred embodiments, the congealing point of the C₂₀ to C₆₀ waxfraction obtained by the process of the present invention is from 35 to65° C. The congealing point measures when a wax ceases to flow and maysuitably be determined by ASTM Method D938.

In preferred embodiments, the needle penetration at 25° C. of the C₂₀ toC₆₀ wax fraction obtained by the process of the present invention isfrom 40 to 100, preferably from 50 to 80. The needle penetrationmeasures the hardness of the wax and may suitably be determined by ASTMMethod D1321.

In preferred embodiments, the kinematic viscosity at 100° C. of the C₂₀to C₆₀ wax fraction obtained by the process of the present invention isfrom 3 to 10 mm²/s (3 to 10 cSt). Kinematic viscosity represents theresistance to flow of a molten wax at the test temperature and maysuitably be measured by ASTM Method D445.

Waxes obtained from the pyrolysis of plastic polyolefin polymerstypically comprise more double bonds than, for instance, polyolefinwaxes formed by high-pressure polymerisation. Determination of the typeand level of double bonds in the wax product may be undertaken, forinstance, by infrared analysis. Meanwhile average olefin content of thewax may be determined from a combination of NMR analysis and simulateddistillation (SimDist) GC. Bromine number may also be measured todetermine olefinicity, in accordance with ASTM D1159.

The wax product of the process of the present invention may undergofurther treatment depending on the desired end use. The wax product ofthe process of the present invention has a number of different usesincluding: fillers in pigment master batches; rub resistance and slipagents in printing inks; additives for paints and coating for increasingscratch resistance; as lubricants and release agents in molding; ascomponents of polishes and varnishes; as hotmelt coatings; ashydrophobic components of corrosion protectants; in toner preparations;as components of insulating materials; and in candles. The wax productof the present invention may also be conveniently converted into alubricant base stock.

Where wax products are obtained from conventional biomass pyrolysis,subsequent conversion of the wax to a lubricant base stock requires ahydrotreatment followed by isomerization. Hydrotreatment removesheteroatoms such as N, S and O, which are undesirable in the lubricantbase stock since they normally give rise to colour instability, andeliminates double bonds. Meanwhile, isomerization selectively transformslinear paraffins to multi-branched isoparaffins, which improveslubricant properties such as pour point and viscosity index.

It will be appreciated that where a mixed feed comprising polypropyleneis used the increase in the amount of branching in the waxes obtainedfrom the pyrolysis reaction can make the isomerization step less energyintensive, i.e. such that the isomerization may be conducted at a lowertemperature than is typically used. For example, the isomerizationreaction may be conducted at a temperature of from 200° C. to 400° C.,preferably from 200° C. to 300° C.

Furthermore, the increase in the amount of branching in the waxesobtained from the pyrolysis reaction can reduce the hydrogen consumptionduring hydroisomerization. In this way, the hydrogen to liquid wax ratiomay be lower than is typically used, as a result of a lower hydrogendemand, allowing for a more efficient hydroisomerization process. Forexample, the hydrogen-containing gas feed rate to the hydroisomerizationreactor may suitably be such that the hydrogen to liquid wax ratio isfrom 100 to 1,750 m³/m³, preferably from 100 to 700 m³/m³, and morepreferably from 150 to 600 m³/m³, for example 175 to 450 m³/m³.

As will be appreciated, in addition to increasing the efficiency of thehydroisomerization step, lubricant base stocks produced byhydroisomerization of the waxes obtained according to embodiments of thepresent invention have desirable properties such as improved pour pointand viscosity index. Lubricant base stocks produced from waxes obtainedaccording to embodiments of the present invention also displayfavourable Noack volatility.

The presence of heteroatoms in wax products obtained from conventionalbiomass pyrolysis is derived, for instance, from the oxygen atomsincorporated in the lignocellulosic constituents of the biomass and sothese must be removed as part of the conversion process. Wax productsderived from natural petroleum sources also contain quantities ofsulphur and nitrogen compounds which are known to contribute to thedeactivation of wax hydroisomerization catalysts. To prevent thisdeactivation, it is preferred that the wax feed to thehydroisomerization reaction contain less than 10 ppmw sulphur,preferably less than 5 ppmw sulphur and less than 2 ppmw nitrogen,preferably less than 1 ppmw nitrogen.

In contrast, the wax product obtained from the thermal decomposition ofplastic polyolefin polymer in accordance with the present invention issubstantially free of heteroatoms and therefore hydrotreatments forremoving heteroatoms may be rendered completely redundant. As will beappreciated, the process of the present invention does not require thepresence of biomass in the plastic polyolefin polymer feed, and it ispreferred that co-processing of plastic polyolefin polymer and biomassis not conducted as part of the process of the present invention. Thus,use of the wax product obtained from the process of the presentinvention may obviate conventional hydrotreating processes and make theconversion of the wax into a lubricant base stock more efficient. As theskilled person will appreciate, content of heteroatoms in the wax may beverified by GC-NPD or chemiluminescence.

Lubricant base stocks may be classified as Group I, II, III, IV and Vbase stocks according to API standard 1509, “ENGINE OIL LICENSING ANDCERTIFICATION SYSTEM”, September 2012 version 17^(th) edition AppendixE, as set out in the table below:

Saturated Sulphur content hydrocarbon (% by weight) Viscosity contentASTM D2622 or Index (% by weight) D4294 or D4927 ASTM Group ASTM D2007or D3120 D2270 I <90 and/or >0.03 and ≥80 and <120 II ≥90 and ≤0.03 and≥80 and <120 III ≥90 and ≤0.03 and ≥120 IV polyalphaolefins V all basestocks not in Groups I, II, III or IV

Preferably, the lubricant base stock preparable from the wax product ofthe present invention is a Group III/Group III+ base oil. As the skilledperson will appreciate, Group III+ base oils correspond to Group IIIbase oils with particularly high viscosity index (for example, at least135 as measured by ASTM D2270).

The present invention will now be illustrated by way of the followingexamples and with reference to the following figures, wherein:

FIG. 1 : shows a schematic diagram of a vacuum pyrolysis process forproducing a C₂₀ to C₆₀ wax as part of the process of the presentinvention;

FIG. 2 : shows a schematic diagram showing fractionation and downstreamprocessing of the C₂₀ to C₆₀ wax to produce a lubricant base stock;

FIG. 3 : shows a plot illustrating the effect of pressure in thepyrolysis reactor on the thermal decomposition product distribution frompyrolysis of polypropylene in terms of boiling point of constituents;

FIG. 4 : shows a bar graph illustrating the effect of pressure in thepyrolysis reactor in the pyrolysis of polypropylene on the C₂₀ to C₆₀fraction yield;

FIG. 5 : shows a plot illustrating the effect of pressure in thepyrolysis reactor on the thermal decomposition product distribution frompyrolysis of polyethylene in terms of boiling point of constituents;

FIG. 6 : shows a bar graph illustrating the effect of pressure in thepyrolysis reactor in the pyrolysis of polyethylene on the C₂₀ to C₆₀fraction yield;

FIG. 7 : shows a plot illustrating the effect of pressure in thepyrolysis reactor on the thermal decomposition product distribution frompyrolysis of a polyethylene/polypropylene blend in terms of boilingpoint of constituents;

FIG. 8 : shows a bar graph illustrating the effect of pressure in thepyrolysis reactor in the pyrolysis of a polyethylene/polypropylene blendon the C₂₀ to C₆₀ fraction yield;

FIG. 9 : shows a plot illustrating the effect of temperature in thepyrolysis reactor on the thermal decomposition product distribution frompyrolysis of polypropylene in terms of boiling point of constituents;

FIG. 10 : shows a bar graph illustrating the effect of temperature inthe pyrolysis reactor in the pyrolysis of polypropylene on the C₂₀ toC₆₀ fraction yield;

FIG. 11 : shows a plot illustrating the effect of temperature in thepyrolysis reactor on the thermal decomposition product distribution frompyrolysis of polyethylene in terms of boiling point of constituents; and

FIG. 12 : shows a bar graph illustrating the effect of pressure in thepyrolysis reactor in the pyrolysis of polyethylene on the C₂₀ to C₆₀fraction yield.

With reference to FIG. 1 , a plastic polyolefin polymer is supplied toextruder (E1) from a hopper (not shown). The extruder (E1), which inthis instance is heated, produces a molten stream of plastic polyolefinpolymer (101) which is fed to a vacuum pyrolysis reactor (R1) and themolten feed enters the thermal decomposition zone of the reactor (R1).The reactor (R1) is operated at sub-atmospheric conditions and at atemperature to give rise to thermal decomposition of the molten plasticpolyolefin polymer, thereby producing pyrolysis vapours.

The configuration shown in FIG. 1 includes three condensation stages(C₁, C₂, C₃) exemplifying a fractional condensation process. As will beappreciated, the multistage condensation may be operated with only twocondensation stages, or more than three condensation stages, if desired.These pyrolysis vapours produced in the reactor, which may be in theform of an aerosol in which liquid thermal decomposition products areentrained therein, rapidly exit the pyrolysis reactor via an outlet, andthe stream of pyrolysis vapours (102) is fed to a first condensationstage (C₁). The first condensation stage (C₁), which preferably takesthe form of a quench tower, is cooled by means of a circulating liquidcoolant, for example water, or cooled by direct liquid quench, forexample, liquid propane or supercritical CO₂.

At least partial condensation of pyrolysis vapours occurs in the firstcondensation stage (C₁), thereby producing an amount of liquidcondensate, in addition to any liquid thermal decomposition productalready present in the effluent from the reactor. First condensationstage (C₁) includes a collection vessel to hold liquid condensate andliquid thermal decomposition product such that substantially onlyremaining pyrolysis vapours are fed to the second condensation stage(C₂) in stream (103). The condensed product may be extracted from thecollection vessel of the first condensation stage as stream (109) via anoutlet. Stream (109) comprises the C₂₀ to C₆₀ wax fraction, togetherwith any lighter and/or heavier fractions of the condensed thermaldecomposition products. A stream (103), containing remaining pyrolysisvapours, exits the first condensation stage (C₁) and is fed to a secondcondensation stage (C₂).

Second condensation stage (C₂) condenses pyrolysis vapours that have notbeen condensed in the first condensation stage (C₁). The secondcondensation stage (C₂) is preferably cooled by means of a circulatingliquid coolant, for example water, which is at a colder temperature thanthat of the coolant in the first condensation stage (C₁). Condensationof at least a portion of the remaining pyrolysis vapours occurs in thesecond condensation stage (C₂), which may comprise a collection vesselfor holding the condensate. The condensed product may be extracted froma collection vessel of the second condensation stage as stream (110) viaan outlet. Stream (110) primarily comprises lighter fractions of thecondensed thermal decomposition products, for example in the naphthaand/or diesel boiling ranges. This light fraction may be convenientlyused as fuel source for heating the pyrolysis reactor.

Remaining pyrolysis vapours are carried in stream (104) and fed to thethird and final condensation stage (C₃) shown in FIG. 1 . However, asthe skilled person will be aware, additional condensers can also beintegrated into the series of the multistage condensation, which may beof use as a means for improved separation of pyrolysis products as partof a fractional condensation. The third condensation stage (C₃) ispreferably cooled by means of a circulating liquid coolant, for examplewater or glycol, which is at a colder temperature than that of thecoolant in the second condensation stage (C₂), or the precedingcondensation stage if more than three condensation stages are used.Condensation of residual pyrolysis vapours occurs in the thirdcondensation stage (C₃), which may comprise a collection vessel forholding the condensate. The condensed product may be extracted from acollection vessel of the third condensation stage as stream (111) via anoutlet. Stream (111) comprises the lightest fractions of the condensedthermal decomposition products. This lightest fraction may also beconveniently used as fuel source for heating the pyrolysis reactor.

Any non-condensable gas that is present is carried in stream (105) andmay ultimately come into contact with variable speed vacuum pump (V).However, as the skilled person will appreciate, the presence of anypyrolysis vapours is preferably kept to a minimum in this stream andpreferably completely removed by means of the final condensation stage.Nevertheless, the vacuum may be configured to accommodate variousdegrees of non-condensable gases being present in the stream which exitsthe final condensation stage.

FIG. 2 illustrates a possible downstream processing of the wax productof the invention. In particular, the stream (109) is fed to a fractionaldistillation column (F) where a stream (202) comprising substantiallyonly a C₂₀ to C₆₀ wax fraction is produced together with a waste stream(210), which may be either used as a fuel source for the pyrolysisreactor or heavier fractions of this stream may be recycled to thepyrolysis reaction. Stream (202), comprising substantially noheteroatoms, is fed to a hydroisomerization reactor (HI) which isoperated under hydroisomerization conditions in the presence of hydrogenand a bifunctional hydroisomerization catalyst. A stream (203)comprising a lubricant base stock exits the hydroisomerization reactor(HI), is optionally fractionated (not shown) before being fed intosolvent dewaxing unit (DVV) where any residual wax is removed. Productlubricant base stock (204) is thus obtained having both high viscosityindex and low pour point which may be blended to form a commerciallyusable lubricant composition.

EXAMPLES

Preparation of Plastic Feedstock

Pelletized samples of polyethylene (PE) and polypropylene (PP) wereobtained from ADN Materials Ltd. In each of the experiments below,samples of PE, PP or a combination thereof were first pre-melted at 400°C. in a quartz tube reaction vessel under atmospheric pressure for atleast 10 minutes to provide a homogeneous molten material.

General Vacuum Pyrolysis Method

10 g of molten plastic sample was provided in a quartz tube reactionvessel of 24 mm outer diameter and 150 mm length. The reaction vesselwas located inside a Carbolite® tubular furnace of 300 mm length and 25mm diameter with a borosilicate glass still head fitted to the top ofthe quartz tube, which was in turn connected to a distillation condenserand 200 ml 2-neck round bottomed cooled collector flask. Thedistillation condenser was temperature controlled by means ofcirculating oil at a temperature of 80° C. The collector flask wascooled by acetone/dry ice bath (−78° C.) and connected to BuchiRotavapor® membrane pump equipped with a digital vacuum controller.

Pyrolysis of the molten plastic sample began after applying the vacuumto establish sub-atmospheric pressure and increasing the heating topyrolysis temperature. Temperature and pressure conditions werethereafter maintained for one hour, after which the pyrolysis reactionwas complete and no further effluent from the reaction vessel wasobserved. A condensate product was collected in the collector flaskcomprising the wax product.

Example 1

The above general procedure for pyrolysis was followed for a series offour experiments using 10 g samples of the same propylene feedstock.Pyrolysis temperature was set at 550° C. and four different reactionpressures were adopted: i) 10 kPa; ii) 30 kPa; iii) 50 kPa; and iv) 70kPa.

The collected effluent from the pyrolysis reaction (excludinguncondensable gases) for each experiment was analysed by SimDist GCchromatography in order to determine the composition of the productaccording to boiling point and carbon number. The results showing theproduct distribution based on boiling point are represented graphicallyin FIG. 3 whilst the results showing the product distribution based oncarbon number are provided in Table A below and represented graphicallyin FIG. 4 .

TABLE A Pyrolysis pressure 10 kPa 30 kPa 50 kPa 70 kPa C₂₀-C₆₀ (%) 73 5752 37 <C₂₀ (%) 27 43 48 63

FIG. 3 generally illustrates the trend that as pressure inside thepyrolysis reactor decreases, the boiling point of the constituents ofthe thermal decomposition product obtained is increased. The results inTable A (as also illustrated in FIG. 4 ) are consistent in that theyshow that the amount of higher boiling point C₂₀-C₆₀ fraction isgreatest at lowest pressure. This is believed to relate to lowering ofvapour residence time in the pyrolysis reactor as pressure decreaseswhich minimises secondary cracking reactions so that the thermaldecomposition product has higher carbon number and therefore higherboiling point.

The results of Example 1 also demonstrate that pressure conditions ofthe pyrolysis can be adjusted in order to increase the proportion ofC₂₀-C₆₀ wax fraction that is produced.

Example 2

The series of experiments according to Example 1 was repeated exceptthat samples of the same polyethylene feedstock were used in place ofpolypropylene.

The collected effluent from the pyrolysis reaction (excludinguncondensable gases) for each experiment was analysed by SimDist GCchromatography in order to determine the composition of the productaccording to boiling point and carbon number. The results showing theproduct distribution based on boiling point are represented graphicallyin FIG. 5 whilst the results showing the product distribution based oncarbon number are provided in Table B below and represented graphicallyin FIG. 6 .

TABLE B Pyrolysis pressure 10 kPa 30 kPa 50 kPa 70 kPa C₂₀-C₆₀ (%) 74 5747 29 <C₂₀ (%) 26 43 53 71

FIGS. 5 and 6 illustrate the same trends as observed for thepolypropylene experiments according to Example 1 and these results alsodemonstrate that pressure conditions of the pyrolysis can be adjusted inorder to increase the proportion of C₂₀-C₆₀ wax fraction that isproduced.

Example 3

The above general procedure for pyrolysis was followed for a series ofthree experiments using 10 g samples of the same 50:50 mixture by weightof polyethylene and polypropylene feedstock. Pyrolysis temperature wasset at 550° C. and three different reaction pressures were adopted: i)10 kPa; ii) 30 kPa; and iii) 70 kPa.

The collected effluent from the pyrolysis reaction (excludinguncondensable gases) for each experiment was analysed by SimDist GCchromatography in order to determine the composition of the productaccording to boiling point and carbon number. The results showing theproduct distribution based on boiling point are represented graphicallyin FIG. 7 whilst the results showing the product distribution based oncarbon number are provided in Table C below and represented graphicallyin FIG. 8 .

TABLE C Pyrolysis pressure 10 kPa 30 kPa 70 kPa C₂₀-C₆₀ (%) 78 55 28<C₂₀ (%) 21 44 71

FIGS. 7 and 8 illustrate the same trends as observed for thepolypropylene experiments according to Example 1 and the polyethyleneexperiments of Example 2 and these results also demonstrate thatpressure conditions of the pyrolysis can be adjusted in order toincrease the proportion of C₂₀-C₆₀ wax fraction that is produced in amixed blend of plastic feed.

Example 4

The above general procedure for pyrolysis was followed for a series offour experiments using 10 g samples of the same propylene feedstock.Pyrolysis pressure was set at 30 kPa and four different pyrolysistemperatures were adopted: i) 500° C., ii); 550° C. iii) 600° C., andiv) 650° C.

The collected effluent from the pyrolysis reaction (excludinguncondensable gases) for each experiment was analysed by SimDist GCchromatography in order to determine the composition of the productaccording to boiling point and carbon number. The results showing theproduct distribution based on boiling point are represented graphicallyin FIG. 9 whilst the results showing the product distribution based oncarbon number are provided in Table D below and represented graphicallyin FIG. 10 .

TABLE D Pyrolysis Temperature 500° C. 550° C. 600° C. 650° C. C₂₀-C₆₀(%) 39 57 63 70 <C₂₀ (%) 60 42 36 29

FIG. 9 generally illustrates the trend that as temperature inside thepyrolysis reactor increases, the boiling point of the constituents ofthe thermal decomposition product obtained is increased. The results inTable D (as also illustrated in FIG. 10 ) are consistent in that theyshow that the amount of higher boiling point C₂₀-C₆₀ fraction isgreatest at highest temperature. This is a consequence of an increase inthe volatility of higher boiling (higher carbon number) componentsinside the pyrolysis reactor as the pyrolysis temperature increasescoupled with the low vapour residence time in the pyrolysis reactor,which minimises secondary cracking reactions associated with thesehigher boiling point components.

The results of Example 4 also demonstrate that temperature conditions ofthe pyrolysis can be adjusted in order to increase the proportion ofC₂₀-C₆₀ wax fraction that is produced.

Example 5

The series of experiments according to Example 4 was repeated exceptthat samples of the same polyethylene feedstock were used in place ofpolypropylene.

The collected effluent from the pyrolysis reaction (excludinguncondensable gases) for each experiment was analysed by SimDist GCchromatography in order to determine the composition of the productaccording to boiling point and carbon number. The results showing theproduct distribution based on boiling point are represented graphicallyin FIG. 11 whilst the results showing the product distribution based oncarbon number are provided in Table E below and represented graphicallyin FIG. 12 .

TABLE E Pyrolysis Temperature 500° C. 550° C. 600° C. 650° C. C₂₀-C₆₀(%) 49 53 58 65 <C₂₀ (%) 50 46 41 34

FIGS. 11 and 12 illustrate the same trends as observed for thepolypropylene experiments according to Example 4 and these results alsodemonstrate that temperature conditions of the pyrolysis can be adjustedin order to increase the proportion of C₂₀-C₆₀ wax fraction that isproduced.

Comparison of the results in Tables D and E shows that increasingtemperature has a greater effect on the proportion of C₂₀-C₆₀ waxproduced for polypropylene (Table D) than for polyethylene (Table E). Inthis way, by using a mixed feed comprising polypropylene andpolyethylene, an increased benefit may be obtained by operating thepyrolysis at high temperature in terms of yield of the C₂₀-C₆₀ fractionwhich may be obtained, whilst simultaneously retaining the benefitsassociated with the properties of the wax resulting from the presence ofboth polypropylene and polyethylene (e.g. in terms of chain branchingand viscosity).

General Vacuum Pyrolysis Method for Scaled-Up Reactions

Pelletized samples of polyethylene (PE) and polypropylene (PP) wereobtained from ADN Materials Ltd. as for Examples 1 to 5.

The feedstock material is loaded into a pyrolysis reactor vessel whichis then sealed. Nitrogen (N₂) gas is used to purge the reactor, beforeapplication of a vacuum. Three condensers are set to their respectivetemperatures. Condenser 1 is cooled using a Julabo with ethyleneglycol/water to ca. −10° C. Condenser 2 is cooled using ethylene glycoland dry ice to ca. −15° C. Condenser 3 is cooled using dry ice to −78°C.

The pyrolysis reactor vessel is heated to 275° C., held at thistemperature for 1 hour to pre-melt the feedstock before being heated tothe desired pyrolysis temperature. The pyrolysis reactor vessel is heldat this temperature until the reaction is completed. The reaction wasmonitored by four temperature probes, three of which are in the reactorvessel and one of which is positioned for measuring the temperature ofthe vapours coming out of the vessel. The pyrolysis reactor vessel washeated using a heating source comprising 2 heat belts surrounding thevessel. Pyrolysis temperatures referred to hereafter relate to the settemperature of the heating source. Temperature measurements obtainedfrom probes inside the reaction vessel gradually increase to reach theheating source temperature.

In general, the reaction products comprise various hydrocarbon pyrolysisproducts collected in the condensers, char remaining in the reactionvessel and gases (e.g. hydrocarbons having a boiling point below roomtemperature), which are too volatile to be collected in the condensers.The products of each reaction in the first condenser were analysed bysimulated distillation chromatography (SimDist, ASTM D6352). Theproducts found in condensers 2 and 3 were typically found to be boilingbelow the minimum observable in the SimDist method, indicating theylikely consist of hydrocarbon chains between 5 and 9 carbons in length(C₅-C₉).

Example 6

The above scaled-up general procedure was followed for two experimentsusing a 67:33 HDPE:PP by weight feed. Reaction pressure was set at 350mbar and two different reaction temperatures were adopted: i) 450° C.and ii) 600° C.

The collected effluent from the pyrolysis reaction in the firstcondenser for each experiment was analysed by SimDist GC chromatographyin order to determine the composition of the product according toboiling point and carbon number. The results showing the productdistribution in terms of the different fractions collected are shown inTable F below, whilst the results showing the product distribution basedon carbon number for the first condenser are provided in Table G below.

TABLE F 450° C. 600° C. (kg) (mass %) (kg) (mass %) Feedstock in 12.00100.00 12.00 100.00 Condenser 1 10.52 87.67 9.20 76.67 Condensers 2 + 31.19 9.92 1.51 12.58 Char 0.19 1.58 0.87 7.25 Unaccounted (gases) 0.100.83 0.42 3.50

TABLE G 450° C. 600° C. (mass %) (mass %) C₁₀-C₂₅ 67 51 C₂₅-C₃₁ 13 18C₃₁-C₃₆ 8 12 C₃₆₊ 12 19 C₂₀₊ 49 67

The data in Tables F and G illustrate that at higher reactiontemperatures an increased proportion of C₂₀₊ waxes are produced. This isconsistent with the data in Tables D and E, which show the same trend.In addition to the increased proportion of heavier waxes at highertemperature, Table F shows that a larger proportion of lighterhydrocarbons collected in the second and third condensers are alsoproduced at 600° C. compared to 450° C. Thus, at higher reactiontemperatures, not only are more heavy waxes produced, but there is alsoa more defined split in the distribution between heavy and lighthydrocarbons. This leads to an increase in the amount of productcollected in the second and third condensers. In this way, the increasedseparation provided by a multistage condensation is particularlyeffective in combination with a higher pyrolysis temperature, i.e. thereis a certain synergy between the use of higher pyrolysis temperature andthe provision of a multistage condensation in a process for isolating aC₂₀-C₆₀ wax from the pyrolysis process. It will be understood thatconvenient separation of lighter fractions during condensation maysimplify or eliminate the downstream distillation requirements.

Example 7

The above scaled-up general procedure was followed for two experimentsusing a pure HDPE feed. Reaction pressure was set at 350 mbar and twodifferent reaction temperatures were adopted: i) 450° C. and ii) 600° C.

The collected effluent from the pyrolysis reaction in the firstcondenser for each experiment was analysed by SimDist GC chromatographyin order to determine the composition of the product according toboiling point and carbon number. The results showing the productdistribution based on carbon number for hydrocarbons collected in thefirst condenser are provided in Table H below.

TABLE H 450° C. 600° C. (mass %) (mass %) C₁₀-C₂₅ 49 37 C₂₅-C₃₁ 19 13C₃₁-C₃₆ 12 10 C₃₆₊ 20 40 C₂₀₊ 61 69

The data in Table H illustrate that at higher reaction temperatures anincreased proportion of C₂₀₊ waxes are produced. This is consistent withthe data in Tables D, E and G, which show the same trend.

Furthermore, the data in Table H also show that increasing temperaturehas a greater effect on the proportion of C₂₀-C₆₀ wax produced for thesepolypropylene containing feeds (Tables D and G) than for purepolyethylene feeds (Tables E and H). In this way, by using a mixed feedcomprising polypropylene and polyethylene, greater benefits in terms ofyield of the C₂₀-C₆₀ fraction at higher temperature may be obtainedwhilst also retaining the benefits of having a mixture of polypropyleneand polyethylene in the feed in terms of the properties of the resultingwax. Even at temperatures where ultimately less of the C₂₀₊ fraction isproduced for PP containing feeds in comparison to PE feeds, highertemperatures will mitigate the loss whilst retaining the benefits ofincluding some branching in the waxes. Thus, there is a certain synergybetween the use of higher pyrolysis temperature and the use of a certainproportion of polypropylene in the feed for isolating a C₂₀-C₆₀ wax fromthe pyrolysis process with particularly beneficial properties.

Example 8

The above scaled-up general procedure was followed for three experimentsusing an 80:20 PE:PP by weight feed. Reaction pressure was set at 350mbar and three different reaction temperatures were adopted: i) 450° C.,ii) 525° C. and iii) 600° C.

The collected effluent from the pyrolysis reaction in the firstcondenser for each experiment was analysed by SimDist GC chromatographyin order to determine the composition of the product according toboiling point and carbon number. The results showing the productdistribution in terms of the different fractions collected are shown inTable I below, whilst the results showing the product distribution basedon carbon number for the first condenser are provided in Table K below.

TABLE I 450° C. 525° C. 600° C. (kg) (mass %) (kg) (mass %) (kg) (mass%) Feedstock in 10.015 100.00 10.000 100.00 10.010 100.00 (8.005 +2.010) (8.000 + 2.000) (8.005 +2.005) Condenser 1 7.67 76.59 7.575 75.757.200 71.29 Condenser 2 + 3 0.46 4.59 0.695 6.95 0.815 8.07 Char 0.252.50 0.11 1.1 0.210 2.08 Unaccounted 1.635 16.33 1.62 16.2 2.21 18.56

TABLE K 450° C. 525° C. 600° C. (mass %) (mass %) (mass %) C₁₀-C₂₅ 55 5542 C₂₅-C₃₁ 18 17 14 C₃₁-C₃₆ 11 11 16 C₃₆₊ 16 17 28 C₂₀₊ 63 62 69

The results in Tables K and I are consistent with the results in TablesF and G, showing that at higher pyrolysis temperatures there are largerproportions of heavier waxes produced, particularly the C₃₆₊ fraction.As also seen in Table F, Table I also shows an increased amount ofproduct collected in the second and third condensers at highertemperatures, suggesting a certain synergy in the use of a multistagecondensation in combination with higher pyrolysis temperatures inobtaining efficient production and separation of the desirable waxfractions.

The invention claimed is:
 1. A vacuum pyrolysis process for preparing aC₂₀ to C₆₀ wax from thermal decomposition of plastic polyolefin polymer,the process operated as a continuous process comprising the steps of: i)introducing plastic polyolefin polymer into a thermal reaction zone of avacuum pyrolysis reactor on a continuous basis; ii) heating the plasticpolyolefin polymer at sub-atmospheric pressure, wherein a temperature inthe thermal reaction zone of the vacuum pyrolysis reactor is from 500°C. to 750° C., to induce the thermal decomposition of the plasticpolyolefin polymer and to form a thermal decomposition product effluentwhich comprises a major portion by weight of a C₂₀ to C₆₀ wax fraction;iii) condensing a vapour component of the thermal decomposition producteffluent from the vacuum pyrolysis reactor in a multistage condensationcomprising a plurality of condensation stages connected in series,wherein a C₂₀ to C₆₀ wax fraction having a melt point of from 45° C. to80° C., a needle penetration at 25° C. of 40 to 100, and a kinematicviscosity at 100° C. of 3 to 10 cSt, is collected in a firstcondensation stage of the plurality of condensation stages, wherein thefirst condensation stage is operated at a temperature of from 65° C. to120° C. and under sub-atmospheric conditions, and wherein at least aportion of the thermal decomposition product effluent is fed to afractional distillation column; and iii-a) extracting a respectiveplurality of condensed product streams from the plurality ofcondensation stages.
 2. The process according to claim 1, wherein theplastic polyolefin polymer is introduced into the pyrolysis reactor bymeans of an extruder.
 3. The process according to claim 2, wherein theextruder is heated.
 4. The process according to claim 2, wherein theplastic polyolefin polymer introduced into to the extruder is at leastone member of a group consisting of flaked, pelletized, and granularform.
 5. The process according to claim 1, wherein the plasticpolyolefin polymer is in molten form when introduced into the thermalreaction zone of the vacuum pyrolysis reactor.
 6. The process accordingto claim 1, wherein the temperature in the thermal reaction zone of thevacuum pyrolysis reactor is from 500° C. to 650° C.
 7. The processaccording to claim 1, wherein the temperature in the thermal reactionzone of the vacuum pyrolysis reactor is from 525 to 650° C.
 8. Theprocess according to claim 1, wherein the pressure in the thermalreaction zone of the vacuum pyrolysis reactor is less than 75 kPaabsolute.
 9. The process according to claim 1 wherein the plasticpolyolefin polymer comprises or consists essentially of used or wasteplastic.
 10. The process according to claim 1, wherein an opticalsorting process is utilized to obtain the plastic polyolefin polymer ofdesired composition.
 11. The process according to claim 1, wherein theplastic polyolefin polymer comprises polyethylene.
 12. The processaccording to claim 11, wherein the plastic polyolefin polymer comprisespolyethylene and polypropylene.
 13. The process according to claim 1,wherein the multistage condensation according to step iii) includes onlytwo condensation stages connected in series, or wherein the multistagecondensation according to step iii) corresponds to a fractionalcondensation and includes at least three stages connected in series. 14.The process according to claim 1, wherein the first condensation stageis operated as a direct liquid quench.
 15. The process according toclaim 1, wherein a majority of the C₂₀ to C₆₀ wax fraction is collectedin a collection vessel of the first condensation stage.
 16. The processaccording to claim 1, wherein the process further comprises a step iv)of fractionating the thermal decomposition product effluent to obtain aC₂₀ to C₆₀ wax fraction substantially free of lighter and/or heavierthermal decomposition products.
 17. The process according to claim 16,wherein a lighter boiling point fraction separated from the C₂₀ to C₆₀wax fraction in step iv) is used as a source of fuel for heating thevacuum pyrolysis reactor.
 18. The process according to claim 1, whereinthe C₂₀ to C₆₀ wax fraction comprises a mixture of paraffins andolefins, and/or wherein the C₂₀ to C₆₀ wax fraction comprises from 20wt. % to 80 wt. % olefins.
 19. The process according to claim 1, whereinthe C₂₀ to C₆₀ wax fraction comprises at least 50 wt. % of a C₂₅ to C₅₅wax sub-fraction, and/or wherein the C₂₀ to C₆₀ wax fraction comprisesat least 50 wt. % of a C₂₅ to C₅₀ wax sub-fraction, and/or wherein theC₂₀ to C₆₀ wax fraction comprises at least 50 wt. % of a C₃₀ to C₄₅ waxsub-fraction, and/or wherein the C₂₀ to C₆₀ wax fraction comprises atleast 50 wt. % of a C₃₀ to C₄₀ wax sub-fraction, and/or wherein the C₂₀to C₆₀ wax fraction comprises at least 50 wt. % of a C₃₀ to C₃₅ waxsub-fraction.
 20. The process according to claim 1, wherein the thermaldecomposition is conducted in the absence of a catalyst.